1. Field of the Invention
The present invention relates to a portable wireless apparatus, in particular, an antenna technique for portable wireless apparatus, to be more precise, a band widening technique for antenna.
2. Related Art
In portable wireless apparatuses in recent years, a plurality of wireless systems such as W-CDMA (Wideband Code Division Multiple Access) and PDC (Personal Digital Cellular) are mounted and a ground wave TV reception using a wide frequency band is conducted. From the viewpoint of antenna, an antenna operating in a wide band is necessary. It is an important technique for size reduction of the portable wireless apparatus to reduce the size of the antenna.
Under such a context, a planar dipole antenna effectively utilizing a structure of a folding portable telephone is proposed (for example, see Japanese Patent Application Laid-open 2002-377877). A high frequency power supply is installed between conductor plates in two casing, and two conductor plates are used as radiation elements of an antenna. Here, “conductor plate” means a conductor portion used as ground of a circuit board on which a wireless circuit and a data signal processing circuit are mounted.
As a feature of this configuration, the planar dipole antenna is implemented, and consequently wider band characteristics as compared with wire dipole antennas are obtained. Since conductor plates that are originally present in the portable telephone are utilized as radiation elements of the antenna, a separate antenna is not needed, and consequently a small-sized antenna can be implemented.
In the above-described configuration, however, the frequency bandwidth is restricted by the shape of the planar dipole antenna. Therefore, it is difficult to further improve the bandwidth. In the planar dipole antenna, there is a problem that the antenna characteristics change according to the shape of the conductor plates.
Thus, although the conventional technique aims at implementing a small-sized wide-band antenna, there is a problem that the frequency bandwidth is restricted by the shape of the planar dipole antenna. Furthermore, there is also a problem that the antenna characteristics are changed according to the shape of the conductor plates. Besides, there are subjects of raising the efficiency characteristics, raising gain characteristics, raising matching characteristics, raising isolation characteristics, reducing the weight, reducing the cost and increasing the elements.